illustrations and material from internet

1. •When a nerve undergoes degeneration due to action of an
irritant the degenerative process also affects the nerve fiber
of that cell; this is known as descending degeneration.
Degeneration can also begin in the nerve fiber and
progress towards the nerve cell (ascending degeneration).
•When a nerve fiber gets severed from its cell body , the
distal part of the nerve fibre undergoes characteristic
degenerative changes known as Wallerian degeneration.
The axis cylinder disintegrates and disappears. The myelin
sheath also degenerates and is transformed into a chain of
lipoid droplets.

2.  The cells of the sheath of
Schwann proliferate and
get converted into
phagocytes which
remove the remnants of
axis cylinder and the
lipoid droplets. Similar
changes occur in the
proximal part up to the
first node of Ranvier.

3. Regeneration
In a degenerated nerve fiber there are also
attempts at repair. Nerve fiber in the central
nervous system cannot regenerate but the
peripheral nerves regenerate fairly rapidly.
Schwannn cells play a leading role in the
healing of nerves. If the sheath of schwann
is intact, the Schwann cells proliferate and
arrange themselves in both proximal and
distal ends in the form of a tube.

4.  Along this tube new axis
cylinders grow and unite the
two severed ends. They fail to
heal the gap if it is more than
one inch. In such casesthe gap
is filled in by granulation tissue
which originates from the three
connective

5.  tissue coverings of the
nerve and its bundles.
The Schwann cells
proliferate at both ends.
In case of amputation the
axon fibrils coil up to and
form a nodule called
amputation neuroma
which is covered by
fibrous tissue.

6.  When a peripheral nerve is cut degenerative chances
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occur in the neurons. These changes are called Nissl’s
Degeneration in which the cells become enlarged and
the nucleus is pushed to a side .
Chromatolysis of Nissl’s substance occurs after
breaking up. When regeneration of the nerve fiber
starts the neuron tens to return to normal.
Nissl granule reappear n nucleus takes up to a central
position and the cell become smaller.
Repair in a nerve fibre is a prolonged process requiring
10- 12 months for complete healing.
Repair of the nerve. Repair of the nerve fibers of
central nervous system lacking a sheath of Schwann
does not occur.

7.  The Peripheral Nerve System is responsible for the
relaying of messages between the brain and spinal
cord (Central Nervous System) to the muscles, joints,
organs and skin. Many millions of people
unfortunately suffer from varying degrees of nerve
injuries and loss in limb use.

8.  These injuries may be are most commonly caused by
trauma. When a nerve is compressed or injured, a
variety of damage types can usually be found – each
has its own time course for recovery. A simple
compression will recover very rapidly, where as if the
nerve sheath is destroyed, then weeks may be required
for a new insulating lining to be rebuilt.

9.  If the axon itself is disrupted, then a replacement must
be grown from the cut point all the way to the skin or
muscle which happens at a rate of 1-4 millimetres per
day. If the conduit itself is destroyed, then a regrowing
nerve may never find its way past the point of injury
meaning permanent loss. If a muscle loses its nerve
supply, then the muscle nerve receptors disappear
within 12-18 months.

10.  PRIMARY NERVE REPAIR
 INDICATIONS Any nerve which has been completely
transected, If the wound is clean, attempt of the repair
should be taken up immediately.
 If it is grossly contaminated, control infection first.

11.  Equipments
 Finest monofilament sutures, needles, 8/0
polypropylene/ prolene sutures on 3 mm atraumatic
needles and needle holder should be used. Use
ophthalmic forceps and needle holders, and operating
spectacles

12.  Don’t use silk, catgut, human hair, or dexon because
these are irritant. Coarse sutures may cause so much
fibrosis that the nerve will never function again.Find
the cut ends of the nerve. Put his limb in the position
which will help to bring them together.

13.  Trim back both the cut ends of the nerve with a new sterile
razor blade as in A, Usually about 2 mm is enough.
 Match the cut ends in their correct anatomical positions,
without rotation.
 There are usually very fine blood vessels on one side of a
nerve which will enable you to distinguish its two sides.
 Study the cross section of its fasciculi carefully, and get the
two cut ends to match. The exposed nerve must be freed
from the surrounding tissues for some distance proximal
and distal to the site of injury.

14.  Haemastasis is vital during peripheral nerve surgery.
 Try to put all sutures into the outer sheath of the nerve.
 Sutures deep inside it will interfere with its function
seriously. Pass two stay sutures through the outer sheath of
the nerve on either side. Tie them and leave the ends long
(B).
 Carefully hold the two ends of the nerve together, and ask
an assistant to hold the ends in artery forceps. Put one or
two sutures into the front of the nerve (C).
 Pass one of your stay sutures behind the anastomosis (D),
and cross the other one in front of it, so that you rotate the
nerve as you pull them and expose its back (E).

15.  Note:
 (1) Try not to put more than 8 sutures into the nerve,
or there will be unnecessary fibrosis.
 (2) Don’t let any nerve fibres stick out of the suture
line.
 Manage the wound .
 If you are leaving the wound open for delayed closure,
try to cover the sutured nerve with muscle or skin, and
don’t leave it naked in the wound.

16.  If necessary, make relieving incisions, so that you can
move skin over to cover the nerve, or cover it with a
transposition flap,. or, least satisfactorily, cover it with
a split skin graft.
 Splint the patient’s limb in the position which best
relieves tension on the nerve.
 If you fail to do this, the sutures may pull out.

18.  Nerve repair